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Full text of "Metallurgy Of Cast Iron"

MOULDING,    SWABBING   AND   POURING   TEST   BARS.    525
are not rusty or wet from any cause, as this could cause an explosion when pouring a mould. It is well to rub the chills with a very slight coating of coal oil or good machinery oil, where they are not in constant daily use. The " swab " is something that should not be used in moulding test bars, if possible to avoid it, for the reason that if sands are made wetter in some portions of a mould than others, it affects the grain of the iron at that place, making it different from the rest, and hence it may be an element likely to cause erratic results and deception in recording the iron's true strength. If the sand is such that a swab must be used, it should be done with the greatest caution, especially at that part of the mould where the bar will break in being tested. The plan of pulling the patterns out endwise before the cope is lifted off, as devised by the author in his system, makes it unnecessary, with sand at all fit to mould test bars in, to use any water on the joint of the round part of the bar. The swab might be used a little around the gates, but it is best to avoid it if at all possible to make a clean, firm mould without doing so. Construct a swab so that the flow of water can be under perfect control by the lightest squeeze. To insure the stream or drops striking just the part or spot desired to be dampened, a good plan is to insert a piece of one-eighth inch wire, or long, thin nail, through the body of the swab, to project below it about two inches, as a guide to direct the stream. By using this design of a swab, it will be found that only the exact parts desired to be dampened will be affected, and the water will not be scattered all over the mould, making parts like mud, as is often done by the kind of swabs sometimes used.''